The present invention relates to a rotatable eccentric element for continuous adjustment of vibration amplitude, for use in, for example, the roll in vibrating rollers. In particular, the invention relates to a rotatable eccentric arrangement adapted for stepless adjustment of vibration amplitude, comprising a rotatable shaft with an eccentric weight arranged in a fixed manner thereon and a movable weight which is pivotable relative to the fixed weight between a position with maximum amplitude and a position with minimum amplitude for changing the vibration amplitude of the arrangement.
In the packing of earth, asphalt or similar material using vibrating rollers, the best packing effect is obtained initially if the amplitude is high. After the material has been hard-packed, however, the roll starts to move irregularly and bounce on the surface. This impairs the packing and leads moreover to great stresses on the roller. By reducing the amplitude, this is avoided and the degree of packing can be increased further. This regulation can be effected using electronics and hydraulics, under the control of a packing meter mounted on the roller, which continuously measures the firmness (degree of packing) of the surface. Such an arrangement for continuous adjustment of vibration amplitude is described in, for example, SE 443 591.
However, this previously known arrangement is complicated to produce.
It is also desirable to be able to assess and determine the bearing life because this normally varies greatly depending on use. This is due to the tact that the centrifugal force increases with the frequency and the amplitude, and the stress on the bearings, and thus their life also, is dependent on the magnitude of the centrifugal force.
During asphalt packing, the rolls should not vibrate when the roller is at a standstill or changing its direction of travel. The rollers on the market stop the rotation of the eccentric element before the roller stops or changes the direction of travel. If the eccentric element is started and stopped when the amplitude is great, the result is a resonant frequency with undesirable vibrations as a consequence. It is therefore desirable to be able to start the rotation of the eccentric element essentially without amplitude and to be able to provide the amplitude at the desired frequency, that is to say the desired speed of rotation. It is also desirable to be able to adjust to zero amplitude even with full frequency.
It is therefore an object of the present invention to provide a rotatable eccentric arrangement of the type indicated in the introduction, where the abovementioned disadvantages of the known art are completely or at least partly eliminated.
This object is achieved by means of a rotatable eccentric arrangement according to the appended patent claims.